An engine mounted on a vehicle, etc. may include a variable valve timing mechanism for changing the rotational phase of a camshaft with respect to a crankshaft, in which an actuator is attached to the camshaft and is operated by the operating oil supplied from a hydraulic control valve.
JP 2000-199409A [Patent Document 1] teaches variable valve timing mechanism-equipped engines in which the hydraulic control valve is attached to a chain case covering a timing chain for supplying the oil pressure for operating the actuator. Such a variable valve timing mechanism-equipped engine is provided, in the chain case, with an actuator cover section covering the actuator, with a mount installing section for attaching an engine mount, and with the hydraulic control valve below the actuator cover section and the mount installing section. The hydraulic control valve is downwardly and sidewardly covered by a crankshaft pulley and an accessory that is driven by the crankshaft pulley.
In addition, JP 2001-355415A [Patent Document 2] teaches a variable valve timing mechanism-equipped engine, wherein intake-side and exhaust-side actuators of the variable valve timing mechanism are attached to respective intake and exhaust camshafts; intake- and exhaust-side hydraulic control valves are attached to a cylinder head for supplying the operating oil to the intake- and the exhaust-side actuators. In the variable valve timing mechanism-equipped engine, the intake- and the exhaust-side hydraulic control valves are disposed with axes inclined outwardly of the cylinder head in the vicinity of extremities of the intake and the exhaust camshafts.
Problems to be Solved by the Invention
According to the variable valve timing mechanism-equipped engine disclosed in JP2001-355415A, the intake- and the exhaust-side actuators of the variable valve timing mechanism are attached respectively to the intake and the exhaust camshafts; two intake- and exhaust-side hydraulic control valves are attached to the cylinder head for supplying the operating oil to the intake- and the exhaust-side actuators, which complicates the structure of the cylinder head.
To address the problem, attachment of two hydraulic control valves to the chain case can simplify the structure of the cylinder head; however, the installation positions of the two hydraulic control valves are lowered due to the actuator cover section and the mount installing section, contracting the space below the hydraulic control valve and causing the problem of placing the belt for driving the accessory.
Also, when the two hydraulic control valves are respectively disposed at positions opposing to the cylinder block and the cylinder head, operating oil passages for the hydraulic control valves must be disposed both in the cylinder head and the cylinder block, complicating the structure of the operating oil passage.